The social worker didn't coerce anybody. She NOTIFIED the court of a situation that looked like it might constitute child neglect: a boy had what is generally a fatal disease if not treated aggressively, mainstream medical experts agree on what is the best course of treatment in most cases and that multiple rounds of treatment are often necessary; the boy had one round of treatment, didn't like it, and the parents were refusing to follow doctors' advice to repeat the treatment. It's not for a social worker to make a definitive decision in a case like this; her job was to notify the court of her reasonable suspicion that court intervention was warranted. The court intervened, consulted with medical experts, consulted with the parents and nearly-adult child, and the parties came to an agreement that the parents and child are apparently comfortable with.
We'd have a lot more dead children if social workers just blindly ignored worrisome parental decisions. Over the years several children have been killed, and more permanently brain-damaged, by parents who for either religious-whacko or new-age-enviro-whacko reasons insisted on keeping their infants/young children on extremely restricted (usually vegan) diets. When social workers encounter a thin sickly child, whose parents are yakking about stuff like "raw foods only" and "no animal products" and feeding the kid nothing but raw vegetables, it's appropriate for the social worker to alert a court, and for the court to intervene.
"The social worker didn't coerce anybody."
Just to make sure I understand, what you are saying is that if you were in this same situation you would desire to have someone else make this decision for you and your family. For example, if you believed that radiation treatments were the best choice you would rather have a judge decide if that's best or if maybe there was some other therapy he could choose that. You might decide a certain course of action is best but you believe that it would be better to have a judge make the final decision for you.
After all, that is what you are prescribing for this family, so I assume that you would want this for yours as well in a similar situation.